The professor of finance at the University of Pennsylvania's Wharton School maintained his bullish outlook on 2014, telling CNBC on Thursday that he believes the Dow would finish this year at a record high—somewhere between 18,000 and 18,500. His main concern? Getting the jittery retail investor back into the action.

"While I still think there's a push in the markets, I still don't think the public is back," Siegel said on "Squawk on the Street." "I mean they're tiptoeing in, but when you look at the flows into the equity funds, it's not there. ... We have to bring them much more in until we get to the top of a bull market."

The market still has room to grow about 10 to 15 percent next year, but it won't be a straight line, said Siegel, the author of the long-running investment manual "Stocks for the Long Run." It may overshoot estimates, or suffer a correction before hitting fair market value. He said it's normal to be concerned about a strong stock market, especially after the 2008 financial crisis.

"You worry about when there's no risk," Siegel told CNBC. "Bull markets climb the wall of worry. Some of those worries are disappearing."

Siegel's rosy outlook extended to fears over higher interest rates and a bigger emphasis on stock buybacks among corporations. He predicts buybacks will play a large role in the markets this year, and that their use does not mean a company lacks better capital investments.

He also discounted fears that increased borrowing would spike velocity in the money supply to the point where it could hinder the Fed from controlling inflation.

"Short-term rates are going to stay near zero, that's going to keep that velocity down," Siegel said. "We really have to push the economy and inflation to get the velocity up. It's not happening soon."

—By CNBC's Jeff Morganteen. Follow him on Twitter at @jmorganteen and get the latest stories from "Squawk on the Street."